As a representative example of sporting goods wherein a rider places both feet on the board deck while coasting and maneuvering, skateboards are well known.
Now, considering the basic configuration of a conventional skateboard, it includes an elongated oval deck having an area to place both feet thereon, and a pair of rollers rotatably mounted on the underside of the deck at front and rear locations, so that they can roll along the ground.
Disadvantages associated with the conventional skateboard include the fact that the skateboard rider has to push the ground with one foot to achieve additional speed or propulsion when the propulsion of the skateboard is achieved by the rolling of the rollers on the ground. Also, the skateboard inevitably requires a large turning radius when changing the direction of travel or making a U-turn. This results in the need of a large riding space and the rider derives no pleasure from being able to perform delicate movements while riding.
As a solution to improve the conventional propulsion method using the rider's pushing, Korean Patent Registration No. 10-0394848 discloses a skateboard with direction-casters.
The disclosed skateboard comprises a pair of front and rear boards and a connecting element for holding one board at each end and maintaining a predetermined distance between both the boards. At least one of the two boards includes one or more direction-casters attached to the underside thereof. The connecting element is made of an elastic material, so that the connecting element can restore its original shape as soon as any twisting or bending force, applied thereto, is removed.
In operation, in a riding stance with one foot on the front board and the other foot on the rear board, the skateboard rider obtains a propulsive force by alternately leaning both feet to one side or the other side based on a twisting motion of the elastic connecting element. Whenever the rider alternately leans both feet to one side or the other side, the direction-casters rotate back and forth about their respective axes by a predetermined rotating angle. In this case, the components of force of the direction-casters generate a propulsive force which propels the skateboard.
The above-described prior art, however, has the following several problems due to the fact that the two boards are interconnected by use of the elastic element.
Firstly, the two boards, bound with each other via the elastic element, require a large turning radius to change the direction of travel to the left and right or to make a U-turn. Accordingly, changing the direction of travel of the boards has the need of a large space and cannot be rapidly performed. This may be a factor of making the skateboard less safe to use.
Secondly, such a large turning radius as mentioned above makes it impossible for the skateboard rider to delicately maneuver the skateboard.
Thirdly, once the rider places both feet on the two boards, there is no change in the relative positions of feet. Thus, the skateboard provides less exercise than the present invention.
Fourthly, the prior art skateboard has a fixed length. In this case, the skateboard may often be unsuitable for the rider's body size. For example, the skateboard may be too big for small-sized people or too small for large-sized people to conveniently maneuver the skateboard.